Method and composition for making transparent paper



United States Patent U.S. Cl. 106-219 4 Claims ABSTRACT OF THE DISCLOSURE A method and composition for making transparent paper. The paper is impregnated with a composition comprising about 90-91% by weight of paraffin oil, about 9-10% by weight of stearic acid and about 185-233% by weight of abietyl alcohol, wherein the percentages are based upon the total weight of paratfin oil and stearic acid.

This invention relates to a method for making transparent paper and to a composition useful in the practice of the method.

Transparent paper has been known for a long time and is particularly used for drawing paper, lampshade material, and photoreproduction papers for the production of, for example, diazo copies or the like.

In making transparent paper, in actual practice only paper which is absorbent can be used since it must absorb a composition which causes the transparency. Furthermore, it is important that when transparent paper is to be used, as drawing paper or photoreproduction paper, the paper must be very uniformly processed since lack of uniformity is further increased by the composition which is absorbed to make the paper transparent. Normal paper, because of its fibrous structure and the dispersion of light caused thereby, is only slightly transparent.

There are many prior processes for making paper transparent, the specific process depending on the ultimate use. Generally, transparent papers are produced by soaking crude paper with mixtures of natural or synthetic resins and of mineral oils or drying oils, from the melt, with the addition of solvents, or from aqueous dispersions. In the past, processes have also become known in which the raw paper is soaked with a monomer, which is then subsequently caused to polymerize in the paper. The transparency of the paper increases as the impregnation of paper increases, with equal impregnating agent concentration, and as the refraction index of the composition for making the paper transparent comes closer to the refraction index of paper fibers of the paper being made transparent.

To make paper transparent, it is known to use a mixture of petroleum, resinous substances, such as dammar and colophonium, with a trace of vegetable oils, such as castor oil or walnut oil. Also the use of methylor ethyl abietate in combination with sucrose octacetate in a volatile solvent, such as, for example, ethylene chloride, has become known, as well as the use of mineral oil in combination with wax.

It is further known to use solutions of polystyrene resins, cyclo-hexanone resins, chloro-diphenyl resins, alkyd resins, and ureaformaldehyde resins or the like for making paper transparent. According to another known 3,497,370 Patented Feb. 24, 1970 method there is used a one-side coating from the melt or impregnation of a solution with a mixture of polymerized methyl styrene with esters of phthalic acid or sebacic acid. As is well known, it is possible to produce transparent paper by impregnation of an absorbent crude paper with a mixture of cellulose acetobutyrate and chlorinated diphenyl with subsequent coating with a mixture of cellulose acetobutyrate, dibutyl sebacate and butyl stearate.

A great drawback of transparent papers thus produced is that without application of additional layers, the papers are not suitable as underlayers for photosensitive coatings such as photographic silver halide gelatine emulsions, since on the more or less hydrophobic transparent papers the hydrophile photosensitive layers do not adhere sufficiently.

It is therefore an important object of the present invention to provide a method and composition for the pro duction of a transparent paper wherein the disadvantages of known transparent papers are avoided.

It is also an object to provide a method and composition for making transparent paper which does not require additional layers.

My method comprises treating the paper with a composition which comprises an emulsion or a melt of about to by weight of paraffin oil, about 5 to 20% by weight, preferably about 10% by weight of stearic acid, and about 50 to 300%, preferably 200%, by weight of resin alcohol such as abietyl alcohol.

By use of resin alcohol in combination with the paraffin oil and the stearic acid there is avoided a greasing-off or giving off of transparentizing agents to photographic baths and to papers which come in contact with the transparent paper. The percentage of resin alcohol is in reference to the total amount of paratfin oil and stearic acid.

The transparentizing agent according to the invention can be used in the form of a solution of esters and organic hydrocarbons. Also, a melt through which the paper is drawn can be used. It can also be added to the paper as an aqueous emulsion inside of a paper machine.

The paper to be made transparent can be of cellulose fibers or of synthetic fibers or of a mixture of both types of fibers.

The papers produced according to the process of the invention are stable to light, indifferent with respect to photosensitive coatings and stable with respect to photographic baths or chemicals such as are used in diazotypy. There is no reduction of the transparency even with relatively long storage and in processing in photographic baths. The papers produced do not stick together and are practically odorless.

The following examples serve for the explanation of the invention.

EXAMPLE I A roll of photo crude paper of 55 g./m. is drawn at a rate of 20 m./min. through a solution of 20 parts of paraffin oil and 2 parts of stearic acid in a mixture of 60 parts of acetic ester and 13 parts of toluene; and the excess of impregnating agent is stripped off with the aid of scrapers. After the evaporation of the solvent, the paper is immediately suited, without application of additional layers, for coating with photographic silver halide emulsions. The optical density of the transparent paper as measured with the opacimeter of Bausch & Lomb amounts to 0.28. The opacity of the crude paper before the transparentizing was 0.50.

EXAMPLE II A role of crude paper, 80 g./m. is drawn at a rate of m./min. through a solution consisting of Paratfin oil-12.7% (90.7% based *upon total weight of paraifin oil and stearic acid).

Stearic acid1.3% (9.3% based upon the total weight of paraffin oil and stearic acid).

Resin alcohol (abietyl alcohol)26.0% (185% based upon the total weight of paraffin oil and stearic acid).

Acetic ester-45.0%.

Toluene-15 .0

The excess of impregnating agent is stripped off with the aid of Scraper blades. After the evaporation of the solvent the impregnated paper stood for a few days in order to give the impregnating agent situated on the surface of the paper an opportunity to diffuse into the hollow spaces in the paper formerly occupied by the solvent. The optical density of the transparent paper is 0.40 and that of the crude paper is 0.64.

EXAMPLE III A photographic crude paper of 55 g./m. is drawn, after the sheet formation on the paper machine, with a dry content of about 60%, through an emulsion consisting of parts of paratfin oil, 2 parts of stearic acid, 2 parts of Emulsogen A (a trademark of Anorgana GMBH of Gendorf, Upper Bavaria, a fatty acid polygolycol ester recommended for emulsifying mineral oils and fatty oils) and 76 parts of water. The excess impregnating agent is squeezed out by rubber rollers. The paper is then dried within the paper machine to a moisture content of about 6% of water. The optical density of the impregnated paper amounts to 0.32.

EXAMPLE IV A photographic crude paper of 55 g./m. is drawn through a melt which consists of 70% (233% based upon the total weight of parafiin oil and stearic acid) of resin alcohol, 27% (90% based upon the total weight of paraffin oil and stearic acid) of paraffn oil and 3% (10% based upon the total weight of paraffin oil and stearic acid) of stearic acid. The excess of impregnating agent is stripped off with the aid of scrapers heated to C. The optical density of the transparent paper is 0.18 and that of the crude paper is 0.50.

I claim:

1. A method for making transparent paper comprising the step of impregnating paper with a composition comprising about -91% by weight of paraflin oil, about 910% by weight of stearic acid, and about 185233% by weight of abietyl alcohol, said percentages being based upon the total Weight of parafiin oil and stearic acid.

2. The method of claim 1 wherein about 10% by weight of stearic acid and about 200% by weight of abietyl alcohol are used.

3. A composition useful for producing transparent paper, said composition comprising about 90-91% by weight of parafiin oil, about 9-10% by weight of stearic acid and about 185-233% by weight of abietyl alcohol, said percentages being based upon the total weight of paraflin oil and stearic acid.

4. The composition of claim 3 wherein about 10% by weight of stearic acid and about 200% by weight of abietyl alcohol are used.

US. Cl. X.R. 

